Tank level Sensor

[powersoff]

I want to read the level of a water in a polytank. The water fills the tank via gravity from a condenser on a roof(lots of turbulence and vibration).
Can anyone recommend a level or pressure sensor with a 4/20mA output for this application?

Thanks

 

[danw2]

Where can an instrument access the tank? top, bottom, low on the side? Access and/or mounting is a major consideration

- Ultrasonic or radar: non-contact, top mounted. Ultrasonic has a dead zone at some distance ( <12") beneath face of the transducer where it can't read the echo signal. I've heard that technically, level-radar is supposed to be used in metal tanks by some federal regulation or other, but the level-radar police do not appear to have been very active. If you're next door to an airport they might be, though.

- submersible head pressure: pressure transmitter on a long cable with a vent tube attached for atmospheric reference is dropped into the tank from the top

- bubbler: top mounted; a tube with a v notch in the bottom that bleeds air bubbles from a differential air regulator. The back pressure in the tube equals the head pressure of the column of water. Requires continuous stream of dry air.

- capacitance: a rod inserted from the top measures level due to capacitance of water. Plastic tanks require a metal reference rod as part of the inserted rod assembly.

- pressure transmitter: plumbed to an access port near the bottom of the tank, reads the head pressure above the elevation of the access port (assuming transmitter is at same elevation as the access port)

- bypass sight gauge: plumbs to bottom or low side of tank. Magnetic float flips a series of visual indicator flags. All vendors offer some sort of optional electronic gizmo for creating a 4-20mA signal.

- level by weight
load cells weigh the tank and its contents, electronics subtract out the weight of the tank, leaving the weight of the water. Those never-tiring electronic gnomes do some arithmetic on tank dimensions to create a level value.

http://tinyurl.com/2f9cwww

- level by strain gauge
I've never used this and I don't know if it's even advertised to work on plastic, but the idea is to attach at strain gauge to the side of the tank and the distortion of the tank wall with increasing level is sensed by the strain gauge.

 

[xJAyx]

With a lot of splashing and sloshing around I would suggest using a pressure transducer, either hanging in the tank near the bottom, or insterted near the bottom of the tank on a port or flange. There are hundreds of pressure sensors with 4-20mA outputs 1 psi is 27" of head with water.
Ultrasonic would be your next best bet, and some can be found with filters. Milltronics and greyline could be good options.

 

[jraef]

Can you insert a rod with a float?
Balluff magnetostrictive linear transducers with floats


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[roydm]

Plain old DP transmitter will be the simplest and most reliable.
I assume you have an outlet on the bottom just connect it there. Mount the transmitter either below or at the centerline of outlet.
Is freezing a problem?
Is it an open tank i.e. not under pressure?

 

[LeviGarrett]

Emerson Rosemount 3301 Guided Wave Radar

Just used one, works great, easy to program, and comes with RCT software.